An apparatus for cable-twisting two yarns is described in commonly owned and copending applications 886,802 and 899,735 respectively filed 15 Mar. and 25 Apr. 1978 now U.S. Pat. Nos. 4,180,967 and 4,163,357, respectively. In these devices a pair of yarns are wound together and the thus doubled yarn is wound onto a yarn package. The package is rotated at a generally constant peripheral speed by means of a drive roller which peripherally engages it. The yarn is fed through a yarn eye to this yarn package and the yarn eye itself is reciprocated along the package so as to distribute the yarn evenly over the entire package.
It is essential that the yarn not be wound tightly and evenly in this package, but that instead it be wound in an irregular manner, although normally with a constant tension. Such a package is frequently later treated by immersion in a dye or other treatment liquid, so that it is essential that the package be somewhat irregularly wound in order to ensure good penetration of the treatment fluid. Furthermore it must be possible to wind the yarn off the package very easily, for subsequent treatment of the yarn, or weaving or knitting with the yarn.
In the simplest system for achieving this uneven winding, the yarn eye is reciprocated at a regular or sinusoidally regular speed and the drive roller for the takeup spool is similarly driven at a constant speed. This drive roller is, however, periodically lifted slightly from engagement with the package it is driving, so that the peripheral speed of this package varies somewhat. The result is the desired uneven winding in most cases. The same effect can be achieved, of course, by varying the drive speed for the drive roller of the yarn package. Such a system is not, however, useful in conjunction with a twisting machine which must operate at a constant takeup speed in order to ensure regular twisting of the yarns.
German published application No. 2,353,234 describes a system different from that described above wherein the peripheral speed of the yarn package is maintained constant so that it can be used with a yarn-twisting apparatus, and wherein the reciprocation rate of the yarn eye is made irregular in order to produce the desired irregular winding. This arrangement drives the yarn eye by means of a cam follower engaging a cam that is rotated by means of a sun gear in turn engaged by a planet gear carried on a planet carrier that is rotated at a constant speed by means of a constant-speed input gear. The planet gear can rotate in the planet carrier and is connected via an entrainment element to a continuously rotated control wheel in such a manner that the rotation rate of the planet gear is varied to change the rotation rate of the cam and, hence, the reciprocation rate of the yarn eye. To this end the drive shaft for the system has two relatively rotatable gears next to each other and each meshing with a respective driven gear in such a manner that the driven gears are rotated at different speeds. The gear farthest from the cam is provided with an axial cam lobe which, seen radially from the side, rises on one half of its periphery and falls on the other half of its periphery. The gear closer to the cam is axially slidable in a groove of a spring-loaded link which carries on its end turned toward the cam lobe a roller which is provided on its other end with a sawtooth formation. A pawl on the cam has an inclined groove that mates with the sawtooth formation on the link. Since the roller is pressed by the spring-loaded link against the cam lobe and since the gears rotate at different speeds the link moves back and forth in the inclined groove of the pawl. This motion of the link accelerates or slows the rotation of the cam corresponding to the slope of the cam lobe.
In practice it has been found that this continuously and smoothly increasing and decreasing of the reciprocatin speed of the yarn eye does not always avoid the formation of patterns in the yarn being wound onto the yarn package. In particular when large-diameter yarn packages are being wound the periodically increasing and decreasing reciprocation rate for the yarn eye can cause the formation of relatively dense patterns that make subsequent fluid treatment and unwinding of the yarn package quite difficult.
In published German patent application No. 1,535,081 another arrangement is provided wherein a plurality of planet gears journaled in an annular planet-gear carrier mesh on one side with the sun gear of the cam and on the other side in a ring gear having inner and outer arrays of teeth. The planet-gear carrier is journaled on the sun gear and the ring gear on the planet-gear carrier. The ring gear of the planetary gear transmission is driven by means of a drive gear directly on the drive shaft. The control wheel is also driven by a gear mounted directly on the drive shaft and the rotation speeds are such that the control wheel rotates at a rate which is slightly different from that of the ring gear. In this arrangement the entrainment element is formed by a plate between the planetary-gear arrangement and the adjacent gear, this plate being fixed on the ring gear and being slidable therein. The plate carries an entrainment bolt which engages in a radial groove of the planet-gear carrier. The gear adjacent the planetary-gear transmission is provided with an eccentric hub to which is affixed a grooved control ring. A cam follower is engaged in this control ring and is connected to the entrainment plate. The control ring can be fixed at different angles by means of latching bolts relative to the eccentric hub so that the eccentricity of the groove, relative to the axis of the ring gear, can be set larger or smaller. As a result of the differential in speed between the ring gear and the adjacent gear and as a result of the eccentricity of the grooves the entrainment plate is shifted slowly inside the guide. As a result of this radial displacement relative twisting is transmitted by the bolt between the planet-gear carrier and the ring gear. This twisting is transmitted to the eccentric and, in accordance with the position of the entrainment of the plate, the reciprocation rate of the yarn eye increases and decreases continuously.
Once again this continuous increasing and decreasing of the reciprocation rate for the yarn eye ensures that adjacent turns of the yarn on the package will not be exactly parallel. These turns will, however, be close to parallel and in a large-diameter spool will, once again, produce some patterned winding. Furthermore the above-described equipment is relatively complex and failure-prone.